Typical antifuse devices used in complementary metal-oxide semiconductor (CMOS) technology utilize one or more layers of electrically insulating materials including undoped silicon (Si), stoichiometric silicon nitride (Si3N4 also referred to as SiN1.33) and silicon dioxide (SiO2). To maintain compatibility with standard CMOS circuitry, the write voltage used to program an antifuse by breaking down the insulating material therein should be less than 10 Volts, and preferably less than 5 Volts. Since the breakdown electric field EBD for stoichiometric silicon nitride can exceed 10 MV-cm−1, an overall layer thickness for the stoichiometric silicon nitride needs to be less than 10 nanometers (nm). At this layer thickness, electrical conduction in the stoichiometric silicon nitride is dominated by Fowler-Nordheim tunneling rather than by Poole-Frenkel emission. As a result, the onset of electrical breakdown in the thin stoichiometric silicon nitride insulating layer is not due to a well-defined threshold field phenomenon so that a breakdown electric field distribution becomes broadened. One effect of this is that a random occurrence of low-field electrical breakdown events is manifested with breakdown voltage values which can sometimes occur below a specified write voltage for the antifuse. This has obvious detrimental ramifications on circuit reliability.
The present invention overcomes the prior art by providing an antifuse in which the thickness of an electrically-insulating layer can be made sufficiently large for Poole-Frenkel emission to be the dominant mechanism for electrical conduction, while at the same time providing a breakdown electric field EBD which can be adjusted independently of the thickness of the electrically-insulating layer. According to the present invention, this can be done by providing in the electrically-insulating layer a single non-hydrogenated silicon-rich silicon nitride layer whose composition SiNX can be selected to provide a breakdown voltage of generally ≦10 Volts, and preferably ≦5 Volts. The non-hydrogenated silicon-rich silicon nitride layer used according to the present invention is a non-stoichiometric composition of silicon nitride which is essentially-hydrogen-free and which has a nitrogen content X which is generally in the range of 0<X≦1.2, and preferably in the range of 0.5≦X≦1.2.
These and other advantages of the present invention will become evident to those skilled in the art.